🚀 go-pugleaf

In article <80536@ut-emx.uucp> joe@astro.as.utexas.edu (Joe Wang) writes:
>In article <1992Sep23.143830.25927@cid.aes.doe.CA> ynecgan@cid.aes.doe.CA (Greg Neill) writes:
>>I have repeatedly come across
>>statements similar to: "...the general expansion of the universe does
>>not affect galaxy structure or clusters, since they are held together
>>too firmly by gravitational forces."  Now, what the heck does this mean?
>>Is space not expanding uniformly at all scales?  
>
>Nope.
>
>The calculations that demonstrate that the universe should expand a
>uniform rate ASSUME that you have a universe whose density is uniform.
>Now at large scales, this is a pretty good assmuption.  If you look
>at the universe as a whole, it looks and acts a lot like a uniform
>fluid, just like a air looks and acts a lot like a uniform fluid if
>you don't look closely enough to see atoms.
>
>At small scales, however, the universe is not uniform, and so you have
>to throw any calculations assume that it is out the window.  


So at very small scales, in the viscinity of matter condensations (like
a cluster, star, or solar system) space does not expand.  Where does one
draw the periphery about a clump of matter such that on one side of the 
dividing line space is expanding, and on the other side it is not?  Can 
we get work out of a system spanning such a boundary, effectively tapping
energy directly from the Big Bang itself?

Looks like the universe is "blowing bubbles", since we would expect the
large voids to expand while "connected" features like Great Walls would
not...although I suppose the Walls would eventually be stretched mighty
thin.  This presumes, of course, that the expansion continues
indefinitely.  A closed or flat universe would demonstrate some limiting
overall density.
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